The major objective of this research is to investigate, in greater depth, the humoral mechanisms involved in the production and release of red and white blood cells. Attempts will be made to determine the specific hematopoietic subcellular receptor sites of radioiostopically-labeled erythropoietin (Ep) and androgenic steroids steroids utilizing electron microscopy and high resolution autoradiography. Additional studies will concern the mechanism of Ep biogenesis with emphasis on the physiological factors influencing production of renal and extrarenal erythrogenin and the plasma substrate with which it intereacts to produce Ep. Further purification of erythrogenin extracted from almost pure populations of renal lysosomes, separated by centrifugation on a linear sucrose density gradient in a zonal rotor, will be attempted. Likewise the chemical nature of the plasma substrate will be probed. Also to be examined is the role of Ep in the Shay chloroleukemia in rats and the influence of Ep on the course of the disease. More efficient methods for evoking the leukocytosis-inducing factor (LIF) are being developed. Further purification of the LIF is planned utilizing chromatograahic, ultracentrifugation and electrophoretic procedures. Mechanisms underlying leukocyte release will be examined in the H3-Tdr pre;abeled intact rat and in similarly prelabeled isolated perfused rat hind legs. Additional studies will deal with feedbackinfluences exerted by specific leukocyte types on leukocyte release.